1. Field of the Invention
The present invention relates to an air bag device for a motor vehicle, and more particularly to an air bag device wherein a peripheral portion of an opening of a hollow air bag, which is to be attached around a gas generator, is reinforced.
2. Description of the Prior Art
Air bag devices have been mounted on motor vehicles for protecting passengers or occupants in the events of an accident.
The air bag device is generally provided with a gas generator mounted on the steering wheel, dash board or the like to discharge gas in the event of an accident, and a hollow air bag having a peripheral portion, defining an opening, which is attached around the gas generator. The air bag is normally housed in a folded condition. In an emergency, gas is discharged from the gas generator to rapidly inflate the air bag.
When the air bag is inflated and a tension is applied to the air bag, the peripheral portion of the opening of the air bag is pulled outwardly with respect to the gas generator. In order to resist this tension and to prevent the peripheral portion of the opening of the air bag from moving outwardly with respect to the gas generator, the conventional air bag devices have adopted various measures.
In one of the conventional air bag devices, one or more reinforcing sheets are sewed to the peripheral portion of the opening of the air bag, and the thus reinforced peripheral portion is fixed to the gas generator by sandwiching it between a retainer and a flange formed around the gas generator.
However, in the above conventional device, the air bag must be firmly clamped by the retainer and the flange in order to resist the above-described tension. Accordingly, the retainer and the flange must each have both a high stiffness and a large thickness.
Another conventional air bag device provided with means for resisting the tension, is disclosed in U.S. Pat. No. 4,793,631.
In this conventional device, as shown in FIG. 7, a peripheral portion 2b of an opening 2a of a hollow air bag 2, which surrounds a gas generator 11, is firmly sandwiched between a back holder 22 fixed to the gas generator 11, and an annular retainer 23 by means of rivets 24.
Stitches 26 are formed in the peripheral portion 2b of the air bag 2 along an end 25 of the annular retainer 23 so as to project into the air bag 2. In an accident, the projecting stitches 26 are brought into contact with the end 25 of the annular retainer 23, thereby intending to resist the tension which is applied to the peripheral portion 2b of the inflated air bag 2. However, these projecting stitches 26 do not have a height and a stiffness sufficient to resist the above described tension, and accordingly cannot sufficiently attain their object.